The traditional procedure for identifying organisms involves comparing the physical characteristics of a collected specimen with the characteristics for a known species. There are numerous taxonomic books that describe the physical appearance, both externally and internally, of millions of species, as well as what is known about their habitats and general biology. Census researchers study collected specimens, often through microscopes, to distinguish features such as the number of tentacles on a jellyfish or the length of spines on a deep-sea anglerfish, and match what they find with existing species descriptions.

The image above contains species of worms. The diversity of marine species demonstrates the difficulty of taxonomic identification. (Natural Geography in Shore Areas - NaGISA. Tetsuya Kato; see full-size image -- 109K)